The present invention relates to a system for transmitting electrical signals between two devices which are connected by a set of contacts which both allow various signals to be transmitted in one or the other direction and allow electrical energy to be supplied to one of the devices from the other.
In a commonly-assigned copending U.S. patent application Ser. No. 920,690, filed June 30, 1978, by Georges M. Giraud, now U.S. Pat. No. 4,217,572, and entitled ARRANGEMENTS FOR TRANSMITTING ELECTRICAL SIGNALS BETWEEN TWO DEVICES WHICH ARE CONNECTED BY CONTACTS, there is described an arrangement which enables various electrical signals, namely data signals, data read-out signals and synchronizing clock signals, to be transferred by means of only two contacts.
When the system described in the above Giraud U.S. Pat. No. 4,217,572 is applied to a system for keeping account of predetermined homogeneous units using an article such as a credit card carrying information, and external means for imprinting and/or operating on the said information, of the kind described in French patent application No. 77 09822 which was filed in France by the present applicants on Mar. 31, 1977, and in corresponding commonly-assigned U.S. application Ser. No. 889,517, filed Mar. 23, 1978, by Giraud et al, and entitled A SYSTEM FOR KEEPING ACCOUNT OF PREDETERMINED HOMOGENEOUS UNITS, one of the two devices concerned is formed by the article and is supplied with electrical energy at two different voltages, one of which, termed V1, is intended to power the logic circuits and the other of which, termed V2, is intended for programming the memory of the device. While the transfer of the various electrical signals between the two devices takes place via only two contacts, it is necessary to provide two other contacts separate from the first two to supply the voltages V1 and V2 to the information carrying article.
Accordingly, it is an object of the present invention to reduce to two the number of contacts which make the connection between the two devices, these two contacts enabling both the various electrical signals to be transmitted in either direction and electrical energy to be supplied to one of the devices, in the present case the article, from the other device.